Accident Overview
A flight instructor was demonstrating a touchdown autorotation to a pilot receiving instruction. The helicopter touched down in a "normal run-on landing configuration." During the forward ground run, the student pilot applied aft cyclic at an altitude of about 15 feet above the ground. The flight instructor immediately moved the cyclic to neutral and lowered the collective as quickly as possible to reduce ground speed.
Sequence of Events
According to the flight instructor, the helicopter then "jumped" up, yawed to the left, and spun approximately 150 degrees before coming to rest. The instructor felt abnormal vibration in the cyclic and collective controls. Upon opening the door to inspect the helicopter, he observed that the main rotor had struck the tailboom.
Damage
The helicopter sustained substantial damage to the tailboom. No preaccident mechanical failures or malfunctions were reported that would have precluded normal operation.
Weather Conditions
The automated weather observation station located 12 miles north of the accident airport reported that, about 17 minutes prior to the accident, the wind was from 220 degrees at 7 knots. The helicopter landed on runway 18.
Relevant Guidance
The Federal Aviation Administration's Helicopter Flying Handbook (FAA-H-8083-21A) includes a section on autorotation that advises: after touchdown, lower the collective to the full-down position. It warns against using aft cyclic to stop forward ground run, as this can allow the main rotor blades to strike the tail boom. Instead, lowering the collective slightly during the ground run places more weight on the undercarriage, slowing the helicopter.